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Molland photography
Participating Frequently
December 16, 2021
Question

why is exposure compensation in Photoshop different (and less good) than in Lightroom???

  • December 16, 2021
  • 2 replies
  • 1421 views

I came across a strange phenomena which you can easily replicate yourself..

As subject, I used coulorful X-mas cards with the top half covered by a grey-card.

As a test I took two images correctly (raw file, tripot, the lot).

The first with correct exposure (measured on the grey card)

The second with +2 stops (i.e. 2 stops over-exposed)

 

In lightroom I made a virtual copy of the over-exposed one and compensated exposure with -2. So this is now correctly exposed, and it looks very much like the correct exposed one (good job Lightroom!).

 

Now the underexposed original is imported into Photoshop. In photoshop an adjustment layer is added with setting -2. One would expect the same result as in Lightroom, but it is not.. it is much worse.

 

In the attached examples you find the difference, each time on the left the correct exposed image, on the right the image with exposure correction, once with LR once with PS.

From the greycard you can see that the exposure-compensation was done well (same brightness).

Now my questions are:

- Why is there a difference in exposure correction in PS and LR.

- What exactly causes it (what is the difference in calculations?)

- Why is it worse in PS; which should be the photo manipulation tool of choice?

 

This topic has been closed for replies.

2 replies

Stephen Marsh
Community Expert
Stephen MarshCommunity Expert
Community Expert
December 16, 2021

In Lr you are working on raw data. In Ps you are working on rendered data. If you performed the same adjustment in camera raw plugin on the raw camera file you should get the same correct result.

    M
    Molland photographyAuthor
    Participating Frequently
    December 16, 2021

    I don't see why that matters.

    My raw data (Nikon D800) is 14 bits, and I import in in PS as 16 bits image.

    So all the colour information that is in the raw data is also in the PS image.

    It is probably correct that the raw plugin works the same as lightroom, but that stil does not expain why the exposure is so different when applied in PS itself.

    Conrad_C
    Community Expert
    Conrad_CCommunity Expert
    Community Expert
    December 16, 2021
    @Molland photography wrote:

    I don't see why that matters.

    My raw data (Nikon D800) is 14 bits, and I import in in PS as 16 bits image.

    So all the colour information that is in the raw data is also in the PS image.

     

    Sure, all the colour information is there, we agree.

     

    What we’re saying is that the structure and nature of the color is different between raw in Lightroonm Classic and the non-raw result converted to a Photoshop document, so combined with the fact that it is probably not the kind of image that Exposure in Photoshop was designed for (as I described in my reply), you get different results.

      Conrad_C
      Community Expert
      Conrad_CCommunity Expert
      Community Expert
      December 16, 2021

      I am not sure what the exact technical answer is, but I can think of two reasons why it might not work the same way.

       

      In Lightroom Classic: The Exposure option is intended for general use like you said, for basic exposure compensation, on all kinds of images. If you’re editing a raw file, then the exposure compensation is applied to the raw data. 

       

      In Photoshop: The Exposure adjustment is not intended for general use. The help page for Exposure says:

       

      The Exposure and HDR Toning adjustments are primarily designed for 32-bit HDR images, but you can also apply them to 16- and 8‑bit images to create HDR-like effects…Exposure works by performing calculations in a linear color space (gamma 1.0) rather than the current color space.

       

      Also, because a normal Photoshop layer is not raw data, the adjustment is being made to data already rendered into RGB channels.

       

      So if your Christmas card in Photoshop is not a 32 bits per channel HDR image, or you are not trying to achieve an HDR-type look, or you are not intending the adjustment to happen in a linear color space, then the results with the Exposure adjsutment in Photoshop may not be what you expect.

       

      Yes, it’s confusing that the feature with the same name in both applications does different things. For a basic lightness adjustment in Photoshop, you’d want to stick to the adjustments traditionally used for that: Brightness, Levels, or Curves depending on what you’re after.

        M
        Molland photographyAuthor
        Participating Frequently
        December 16, 2021

        I think I start to understand.

        But that then means that Lightroom is not working in a linear colour space.

        I found somewhere that usually images have a gamma of 0,45 and if I add that in PS I get a much better result, although it still falls short of LR.

        So then the question would be which colour space LR is using for the exposure setting..

        Conrad_C
        Community Expert
        Conrad_CCommunity Expert
        Community Expert
        December 16, 2021

        Lightroom edits in the ProPhoto RGB color space at 1.0 (linear) gamma encoding. But note that the histogram and reported values are in ProPhoto RGB with an sRGB TRC (tonal response curve) for easier understanding. For details, see this link to a PDF by another frequent contributor to these forums:

        http://digitaldog.net/files/18Color%20Management%20in%20Lightroom.pdf

         

        The article was written for Lightroom (Classic) 1.0, so some of the other color limitations mentioned (not related to this discussion) were removed long ago. For example, soft-proofing was added a while back.

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